Hanna Instruments HI 504 User Manual

Page 9

• In the second case (pH value not close to the buffer) the

meter will remain in the same state until the reading be-
comes unstable or the calibration mode is quitted.

• For the second buffer value it is possible to choose be-

tween pH 4.01 and pH 10.01 (or pH 4.01 and pH 9.18 if
the NIST set has been selected). Use the

æ or key to

switch between the two possibilities.

• Once selected the buffer, the procedure is the same as for

the first calibration point.

Note

A time-out of 2.5 minutes is present for the pH electrode
response time. During calibration, if the pH reading is not
stable after 2.5 minutes, the device displays twice the scroll-
ing message “time-out”, then shows “WRONG” and it is not
possible to complete calibration.

• At the end of calibration, with the meter set as pH control-

ler, the instrument checks if the offset is between -30 and
30 mV and the slope between 53.5 and 62 mV/pH. If the
values are not within these ranges, the message “OLd
ProbE” scrolls twice across the LCD. The electrode is still
working, but it is necessary to perform a cleaning proce-
dure (see “Electrode conditioning and maintenance” and
“In-line Cleaning” sections) or replace it.

If the offset is outside the -60 to 60 mV range, the “dEAd

ProbE” message will scroll across the LCD and the corre-
sponding error is activated. The electrode has to be replaced
as soon as possible because there is no reliability on the
measured pH values.

One-point calibration

A one-point calibration at a value different from the standard
buffer values is possible by entering the desired calibration
value. This is the actual pH value at the current calibration
temperature.

• Enter the pH calibration mode (no matter if the standard or

NIST buffer set is selected), then press the
SETUP key while the secondary LCD is dis-
playing the first buffer value (pH 7.01 or pH
6.86).

The default buffer set is the one used for last calibration,

even if the procedure was not completed.

• Once confirmed the set of buffer val-

ues, the primary LCD shows the
measured pH value, while the second-
ary LCD displays the first required buffer
value.

Two-point calibration

• Remove the protective cap from the pH

electrode and immerse it into the buffer
solution (e.g. pH 7.01) together with
the Potential Matching Pin and the tem-
perature probe, then stir gently.

Note

The electrode should be submerged ap-
proximately 4 cm (1

’’) in the solution.

The temperature probe has to be located
as close as possible to the pH electrode.

Note

When it is not possible to immerse the Potential Matching Pin
together with the pH electrode in the solution, disable the
differential input by setting setup item I.04 to “OFF”.

• When the reading becomes stable, the

probe indicator will stop flashing (after
about 30 seconds), and if the pH value
is close to the selected buffer, the
“CFM” indicator will start blinking, oth-
erwise the “WRONG” indicator, the pot
and the BUF tags will start blinking.

• In the first case press the CFM key to confirm calibration.

The meter will show the scrolling message “Press CFM again
to confirm the current buffer or right to escape” (to prevent
from confirming the calibration point inadvertently).

Pressing again CFM, the secondary LCD will display the

second expected buffer value.